thoracic spine anatomy table 7.1 concept...

Cook, Orthopedic Manual Therapy: An Evidence-Based Approach, 2/E © 2012 by Pearson Education, Inc., Upper Saddle River, NJ

THORACIC SPINE ANATOMY

The thoracic spine is unique from the cervical and lumbar spine because of the size and

extent of the region and the articulations with the rib cage. The articulation with the rib cage leads to

regional variations in movement patterns and function (1). The upper thoracic spine mimics the

movement and to some extent, the anatomy of the cervical spine and the lower thoracic vertebra

mimics the lumbar spine.

Table 7.1: General Information Regarding the Thoracic Spine Region. Concept

Information

Bones Twelve primary vertebrae, 24 individual ribs, 1 manubrium Number of dedicated Joints

101 joints, 20 (synovial) costotransverse articulations, 24 (synovial) costovertebral articulations, 20 costochondral articulations, 24 (synovial) facet articulations, and 13 intervertebral articulations. Scapulothoracic is considered a joint of the shoulder complex

Anatomical regions 3 distinct regions: upper thoracic (C7-T1 toT3-4), mid-thoracic (T3-4 to T9-10; lower thoracic (T9-10 to T12-L1)

Useful landmarks T5 = Nipple level T7-8 = Epigastric level T10-11 = Umbilical level

Palpation: rule of threes • T1-3 SPs are in the same plane as its own transverse processes (TP)

• T4-6 SPs are halfway between its own TP and the TP of the vertebra below

• T7-9 SPs are in a plane with the TP of the vertebra below • T10 SP is in the plane of the TP below • T11 SP is halfway between its own TP and the TP of the vertebra

below • T12 SP is in the same plane as its own TP

Opening movements Flexion (both sides), side flexion (on the side away), rotation (on the side away)

Closing movements Extension (both sides), side flexion (toward), rotation (toward) Theoretical resting Position

Midway between Flexion and Extension

Theoretical close-pack Position

Extension

Theoretical capsular pattern

Side bend and rotation equally limited


Osseous Structures

The thoracic vertebrae can be subdivided anterior to posterior into three specific regions—

the body, the pedicles, and the posterior structures, such as the transverse and spinous processes

(2). Joint articulations occur at the body of the vertebra and at the posterior structures (Table 7.1).

Figure 7.1: Typical Thoracic Vertebra

The thoracic vertebral body is primarily made of cancellous bone and progressively is wider

from the upper thoracic segments to the lower segments (3,4). The inclination of the end plates

remains constant throughout the thoracic spine even though the posterior height of the vertebral

body increases slightly with caudal progression (3).

Kothe et al. (2) reported that the average pedicle height demonstrated greater variability in

the lower thoracic spine than in the middle thoracic spine. The pedicle is a complex three-

dimensional structure that is filled mostly with cancellous bone (62–79%) for structural rigidity. The


outer cortical shell showed different thickness throughout its perimeter and variations in trabeculae at

disparate levels.

The posterior structures include the transverse processes and the articulations, the facets,

and the spinous processes. The spinous processes angle inferiorly and progressively from the upper

thoracic spine to the mid- to lower thoracic spine. The transverse processes angle posteriorly and

provide the contact points for the facets (5).

The ribs are long, thin bones that are commonly fractured during trauma to the thoracic

region (6) and connect to the thoracic spine anteriorly and posteriorly. Each rib has a convex head

that articulates with the concave facets of the vertebral body (costovertebral joint) and transverse

processes of the thoracic spine (costotransverse joint). The anterior connection is called the costo-

sternal attachment and identifies the two separate articulations of the sternum to the costal cartilage

and the costal cartilage to the rib. The anterior articulation is a flattened, concave depression.

The Intervertebral Disc

The intervertebral disc plays a major role in movement control of the thoracic spine, a much

more significant role than the posterior structures (7). With respect to height, the disc in the thoracic

spine demonstrates less height in ratio to the vertebral body than the cervical and lumbar spines (8).

Additionally, the thoracic disc has a relatively small nucleus pulposus (9).

It is expected that the compliance of the thoracic disc is lost much earlier than the cervical or

lumbar disc (13). Disc space narrowing is common from the third decade of life and disc

degeneration, osteophytes, and subsequent degenerative changes are frequent findings in the mid-

thoracic segment (16).

With respect to intradiscal pressures, Polga et al. (11) found that the positions of standing

upright with 10-kg weights in each arm display the highest pressure versus other positions such as

prone lying, sidelying, sitting with and without flexion, and other variations of standing including

twisting.


Joints

Table 7.2: Joints of the Thoracic Spine. Joint

Information

Intervertebral disc Not frequently studied. High incidence of asymptomatic herniated discs and can be a pain generator

Zygapophyseal (facet) joints

Synovial, planar, diarthrodial joints. All thoracic joints are in the frontal plane and vary between 0° and 30° from vertical. This allows significant movement in all 3 planes

Costovertebral

A synovial joint that allows rolling and gliding. The heads of ribs 2–9 (and occasionally the 10th) articulate with 2 vertebral bodies and the disc

Costotransverse

A synovial joint and is shaped differently according to the thoracic level. In the upper thorax, there is a concave/convex articulation between the convex costal surface and concave TP surface. The costotransverse joints gradually flatten and are more planar in the lower thorax. This change in joint shape allows for more rotation and torsional movement above rib 7 and more planar gliding movement below that level During inspiration, the upper chest wall rises (flexes) in the sagittal plane, whereas the lower ribs widen (abduct) in the frontal plane. During spinal flexion, the rib rotates anterior (posterior elements move superiorly and anterior elements move inferiorly)—an internal torsional movement. During spinal extension, the rib rotates posteriorly (posterior elements move inferiorly and anterior elements move superiorly)

There are variations in the zygapophyseal joints (facets) throughout the length of the

thoracic spine. In general, the superior facets face anteriorly but are not completely aligned in the

frontal plane (12). This angulation is reduced as the thoracic spine descends, culminating at T12. At

T12, the facets face both an inferior and superior a similar orientation of the lumbar spine (12).


Figure 7.2: Zygapophyseal Joints of the Thoracic Spine

The architecture of the facets changes throughout the upper, mid- and lower thoracic

segments. In the mid-thoracic region, the superior and inferior articular processes are curved in both

the transverse and sagittal planes, thus permitting multidirectional movement (13,14). However, the

facet architecture does not dictate or guide a specific, directional coupling movement of the mid-

thoracic region.

Within the transverse plane, the superior facet demonstrates near-sagittal angulation as

compared to inferior facet (12). In the coronal plane, the sagittal angulation of the superior facets

demonstrates a steeper degree with respect to the inferior facets (12).

Each facet demonstrates fibrous annular menisci, which may originate medially from the

ligamentum flavum or laterally from the joint capsule (15). These meniscal folds are hypothesized as

the culprits during an acute thoracic facet lock (16). Additionally, each facet demonstrates

asymmetry from right to left at nearly all levels (12). This may produce abnormalities in range of

motion between the right and the left, although in most cases the differences are small (17).


Rib Cage Joints

There are three primary joints associated with the rib cage—the costovertebral joints, the

costotransverse joints, and the costosternal joints. The costovertebral joint is formed by a convex rib

head with two adjacent vertebral bodies, superiorly and inferiorly. The concave inferior costal demi-

facet of the superior vertebral body and the concave superior costal construction of the inferior

vertebral body provide a synovial attachment to the rib head. The rib head articulates with the lateral

aspect of the intervertebral disc in addition to the two separate vertebral connections. The joint has

two synovial cavities separated by an intra-articular ligament (13). This joint also houses meniscoids

that may be involved during acute costovertebral pain (18).

Figure 7.3: The Costovertebral Joint

Peculiarities regarding the costovertebral joint exist throughout the thoracic spine,

specifically the facet orientation for the articulation of the costovertebral joint. The first thoracic

vertebra has an articular facet for the head of the first rib and a demi-facet for the upper half of the

head of the second rib, yet the ninth vertebra occasionally has no demi-facets below that participate

in the articulation with the head of the tenth rib (14).

The eleventh vertebra has large articular facets that are located on the pedicles of the

vertebra. At the tenth vertebra, the orientation of the vertebral body changes and mimics that of the

lumbar spine (19). The transverse processes shorten and have no articular facet to interface with the


rib. The twelfth vertebra is similar to the eleventh except that the facet orientation is further sagittal,

thus mimicking the biomechanical inclination of the lumbar spine (19).

The costotransverse joint is formed by articulation of the rib tubercle and thoracic vertebral

transverse process. The articulation of the ribs with the transverse processes yields two synovial

capsules, one above and one below articulations with an interarticular ligament that provides stability

(19). The costotransverse joint is highly integrated with vertebral body movement and typically

moves in sequence with the vertebral movement.

Figure 7.4: The Costotransverse Joint Attachment

The width of the anterior cartilage gives rise to two separate anterior costosternal

attachments. The first, the costosternal attachment, consists of the costal cartilage and the

articulation of the sternum; the second, the costorib connection, includes the anterior head of the rib

to the flattened, concave depression of the costocartilage (19).

Ligaments

Several ligaments contribute to the thoracic spine structure and function. These ligaments

are best divided into anterior, lateral, and posterior structures (20). The anterior ligaments consist of

the anterior longitudinal ligament and the sternocostal ligaments (20).

The anterior longitudinal ligament, one of the strongest ligaments of the body, runs the

length of the spine, originating from the cervical atlas, and finally blending into the periosteum of the


sacrum. This ligament lies on the posterior of the body, while the sternocostal ligaments comprise

the anterior aspect of the body.

The sternocostal ligament is a broad, membranous band that originates from the anterior

and posterior aspect of the sternal cartilage of the upper ribs and inserts to the posterior surfaces of

the sternum. The interarticular sternocostal ligament attaches one rib to another with the

fibrocartilage and the connection to the manubrium.

The lateral costotransverse ligaments are subdivided into three ligaments—the superior

costotransverse ligament, the middle costotransverse ligament, and the lateral costotransverse

ligament (19). The superior costotransverse ligament originates on the border of the transverse

process and inserts on the upper border of the neck and angle of the rib. The middle

costotransverse ligament originates between the neck of the rib and inserts on the transverse

process at the same level. The lateral costotransverse ligament originates from the lateral aspect of

the transverse process and inserts on the adjacent rib. The intertransverse ligament is only well

formed within the lumbar region and occasionally demonstrates attachments in the lower thoracic

spine. The ligaments prevent excessive movements of side flexion and rotation (11).

The posterior ligaments include the posterior longitudinal ligament, the ligamentum flavum,

the interspinous ligament, and the supraspinous ligament. The posterior longitudinal ligament

descends along the posterior surfaces of the thoracic vertebra and discs to the insertion point in the

sacrum (20,21). The ligamentum flavum ligaments are paired (right and left) ligaments that insert

upward into the anterior lower third of the vertebral lamina at the level above and originate on the

posterior upper third of the lamina below. The elastic, yellow-colored ligament forms the posterior

wall of the vertebral canal and assists in preventing the synovial capsule and menisci from

entrapment into the facet joints (19–21). The interspinous ligament runs from each spinous process

and controls the movements of flexion. The radiate ligament connects the anterior portion of each rib

with the bodies of the two adjacent vertebrae and the intervertebral fibrocartilage between the

vertebrae. Lastly, the supraspinous ligament is composed of a bundle of fibrous tissue that courses

over the tips of each spinous process inserting in the lumbar region at L3-4 (19,21).


The Nervous System

Within the thoracic spine, the sympathetic nervous system plays an important part in pain,

auto regulation, and perception. There are 12 sympathetic ganglia within the thoracic region. The

thoracolumbar sympathetic fibers arise from the dorsolateral region of the anterior column of the

gray matter of the spinal cord and pass with the anterior roots of all the thoracic and the upper two or

three lumbar spinal nerves (19). Some of the fibers connect with the sympathetic trunk, enter the

white rami, and eventually progress to the prevertebral plexuses.

The sympathetic nervous system is responsible for dilation of the bronchi and pupils as well

as other organ-specific responses. Documented evidence supports the benefit of modulation of pain

and remarkably has a nonlocalized effect. Stimulation of the cervical and thoracic spine has

demonstrated upper extremity changes in pain response (pressure-pain) and a measurable

sympathoexcitatory effect (22–24) that can lead to pain reduction.

Muscles

The paraspinal muscles of the thoracic spine are responsible for both trunk and upper

extremity movements and are a common source of injury and pain. Several studies (25–27) have

found that back extensor strength was negatively correlated with degree of kyphosis, suggesting that

strengthening the thoracic spine should reduce the angle of kyphosis. Additionally, strengthening of

the thoracic spinal musculature also improves scapular dynamics and positively alters the

scapulohumeral rhythm (26).

Summary

• The osseous structures of the thoracic spine include the vertebral body and corresponding

right and left ribs. • The thoracic vertebrae can be subdivided anterior to posterior into three specific regions—

the body, the pedicles, and the posterior structures such as the transverse and spinous processes.

• The thoracic intervertebral disc has less height in ratio to the vertebral body as compared to the cervical and lumbar spine.


• The ribs attach in three joints (costovertebral, costotransverse and costosternal) and are long, thin bones with four primary planes.

• The facets of the spine face anteriorly and within the transverse plane; the superior facet demonstrates near-sagittal angulation as compared to the inferior facet.

• The ligaments of the thoracic spine help reduce spine displacement along with the stability provided by the rib cage.

• A notable component of the nervous system in the thoracic spine is the contribution of the sympathetic nervous system. This system may affect visceral structures as well as joints in the periphery.

• The muscles of the thoracic spine contribute not only to thoracic stability but also to stability of the shoulder girdle.

THORACIC SPINE BIOMECHANICS

Range of Motion

Table 7.3: General Biomechanics and Movements of the Thoracic Spine. Topic

General Biomechanics and Movement

Theoretical coupled motion

Coupling patterns remain controversial although recent studies suggest in the middle and lower thoracic spine, rotation and side bending are coupled to the same side (type II motion). Considerable variability between individuals exists

Range of motion • Flexion = 30–40° • Extension = 20–25° • Rotation = 30° • Lateral flexion = 25°

According to White and Panjabi (28), the combined flexion and extension range of motion in

the thoracic spine is bimodal, superior to inferior. The upper thoracic spine demonstrates a

combined 3 to 5 degrees of flexion or extension that is reduced to 2 to 7 degrees at T5 to T6 and

further increases to 6 to 20 degrees at T12 to L1. Overall, greater range of motion is available in

flexion than in extension. The combined side flexion of the thoracic spine is also bimodal, with

approximately 5 degrees of motion in the upper thoracic region slipping to 3 to 10 for the levels of T7

to T11 then progressing to 5 to 10 at T12-L1. Lastly, combined rotation is purported to be 14

degrees at T1-2, which progressively declines to 2 to 3 degrees combined at T12-L1, mimicking the

movement available in the lumbar spine.


Range-of-Motion Restrictions

Patterns of range-of-motion loss are normal within the thoracic spine. Table 7.4 describes

common losses based on regions.

Table 7.4: Common Movement Restrictions of the Thoracic Spine. Name

Location

Spine-mechanically oriented Common Movement Restrictions in the T/S • T1-2—often have decreased extension (i.e., kyphotic) • T3-7—often have decreased flexion (i.e., often have a flat mid-

T/S) • T8-12—often have decreased extension (i.e., kyphotic)

Rib-mechanically oriented External rib torsion: superior border prominent and tender Internal rib torsion: inferior border prominent and tender

Disease/pathology oriented Scheuermann’s disease (extension), compression fracture (extension), scoliosis (side flexion restriction toward convex side), Dowager’s hump (extension-upper thoracic)

Stabilization

Generally, within the thoracic spine, the inferior articular facets face backward slightly

downward and medially, and the superior facets are nearly flat and are directed backward as well

(14). This alignment, combined with the contribution of the costovertebral and costotransverse joints,

and ligamentous structures, results in significant stability within the thoracic spine (14).

The stability and coordination of movement of the thoracic spine is significantly enhanced

and altered by the rib cage (7). The contribution of the rib cage may increase the load capacity of the

spine by three times the normal amount (7,21). Removal of the rib cage demonstrated pronounced

increases in the neutral zone motions of the thoracic spine and resection of the costovertebral joints

significantly altered the ranges of motion such as lateral flexion and rotation of the thoracic spine

(29).

The thoracolumbar spine is able to tolerate compressive loads of up to 975 Newtons. This

preload can occur without damage or instability if applied in the sagittal plane along the natural


curvature of the spine through estimated centers of rotation (30). The spine was found to be least

flexible and demonstrated less range of motion during axial compression (31).

Coupled Movement

Recently, Sizer and colleagues (31) performed a systematic literature review of coupling

pattern in the thoracic spine. In summary, their study indicates that coupling movements of the

thoracic spine are inconsistent whether the initial movement involves side flexion or rotation. Under

no circumstances are thoracic spine coupling movements predictable. During conditions such as

scoliosis, it is normal to see the spinous processes reflect toward the convexity of the rotation, or

side flexion and rotation that occurs to the same side. This pattern is highly consistent in the upper

thoracic spine and predominates in the mid- and lower thoracic spine but does demonstrate

variability (31).

Summary

• Generally, thoracic spine range of motion is similar but bimodal. The range of motion

declines near the mid-thoracic region but increases caudal and cephalic to the mid-thoracic segments.

• The thoracic spine is very stable, receiving stability contributions from the ligaments, the joints of the rib cage, and the rib cage structure.

• Coupling of the lumbar spine is location dependent. Generally, the upper thoracic spine couples with the lower cervical spine consistently. The mid-thoracic region demonstrates variable coupling, and the lower thoracic region tends to couple with the upper lumbar spine that is also variable.

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